As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is produced by folding and sealing a web of laminated packaging material. The packaging material has a multilayer structure comprising a base layer, which imparts strength and rigidity to the package, and which may be defined by a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material. The base layer is covered on both sides with layers of thermoplastic material, e.g. polyethylene films; and, in the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of oxygen-barrier material, e.g. aluminium foil, which is superimposed on a layer of thermoplastic material, and is in turn covered with another layer of thermoplastic material eventually forming the inner face of the package contacting the food product.
As is known, such packages are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material. The web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, after sterilization, is removed, e.g. vaporized by heating, from the surfaces of the packaging material; and the web of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped packages.
Alternatively, the packaging material may be cut into blanks, which are folded on forming spindles to form the packages, which are then filled with the food product and sealed. An example of this type of package is the “gable-top” package commonly known by the trade name Tetra Rex (registered trademark).
Such packages are normally fitted with closable opening devices to protect the food product in the package from contact by external agents, and to enable withdrawal of the product.
The most commonly marketed opening devices at present comprise a frame defining a pour opening and applied about a removable or pierceable portion of the top wall of the package; and a cap hinged or screwed to the frame and which can be removed to open the package. Alternatively, other types of opening devices, e.g. sliding types, are also used.
The removable portion of the package may be defined, for example, by a so-called “prelaminated” hole, i.e. a hole formed in the base layer of the packaging material before the base layer is covered with the thermoplastic layers and with the barrier layer, which closes the hole to ensure aseptic airtight sealing, while at the same time being easily pierced.
In a known solution described in patent application EP-A-331798, the cap of the opening device is screwed to the frame, and has an inner portion extending through the pour opening and fixed directly to the laminating material covering the hole in the base layer of the packaging material, so that, as the cap is unscrewed off the frame, the removable portion remains attached to the cap and is twisted off the rest of the top wall of the package.
Though relatively practical, the above solution has the drawback that, when twisting off the removable portion, the edge of the laminating material, as opposed to being torn neatly, tends to fray, thus preventing the food product from being poured smoothly.
To eliminate the above drawback, pull-off package opening systems have been designed. One example is described and illustrated in Patent Application EP-A-943549, which relates to a closable opening device substantially comprising an externally threaded, annular frame fixed about the removable portion of the package and defining a circular pour opening for the food product; a removable cap screwed to the frame to close the pour opening; and pull-off opening means housed in the pour opening and defined by a rigid plastic plate, which is glued to the removable portion, is connected integrally to the frame by breakable bridges, and can be pulled off the frame together with part of the removable portion.
In this case, the removable portion is defined by a sealing sheet glued to the outside of the package to close a through hole in the package.
The package is opened by unscrewing the cap from the frame, and then pulling the opening plate out of the frame. Being glued to the sealing sheet, the opening plate, when pulled off, also detaches the part of the sealing sheet attached to it, thus exposing the hole in the package.
Though providing for neater opening of the package as compared with “twist-off” solutions, the above solution still leaves room for further improvement.
In particular, the pull exerted by the opening plate on the sealing sheet stretched tautly over the hole in the package calls for a certain amount of effort, and may result in a ragged initial tear.
Moreover, owing to the opening plate being connected to the frame by a number of breakable bridges, opening of the package is jerky, thus possibly resulting in squirting and spillage of the product.
Finally, in the event the package, with the removable portion detached and the cap put back on, is laid horizontally, e.g. is stored for further use in a refrigerator, continual absorption of the food product, particularly if of an aggressive nature, by the edge of the hole in the packaging material may result, after a relatively long period (eight hours on average), in detachment of the opening device from the package and leakage of the contents.